We recently demonstrated that delivery of physiological amounts of microRNA-145 (miR-145) completely restored impaired coronary collateral growth (CCG) in a rat model of metabolic syndrome by restoring vascular smooth muscle cells (VSMCs) to their normal physiological phenotype (contractile vs. synthetic) in the late stage of CCG. miR-145 is highly enriched in smooth muscle and is expressed at high levels in normal, healthy coronary VSMCs. Its expression is severely decreased in VSMCs of metabolic syndrome animals and humans and correlates with loss of the normal contractile VSMC phenotype. As such this intervention has potentially important implications for clinical re-vascularization therapy. However, to assess the clinical applicability of miR-145-based therapy for induction of CCG, it is essential to understand the mechanisms by which it achieved restoration of CCG. We propose that this single miR delivered to a single cell type (VSMC) had such a profound effect on a complex process of collateral growth, which involves coordinated interactions between multiple cell types, because the miR-145-induced conversion of synthetic VSMCs to contractile VSMCs in turn modulated all key regulatory aspects of CCG including ECM remodeling, endothelial cell (EC) survival and function, inflammatory cell infiltration, and reactive oxygen species (ROS), bioavailability of growth factors vs. growth inhibitors, and nitric oxide (NO). Our data show that VSMC-specific miR-145 delivery converted VSMCs from synthetic to contractile phenotype and normalized (converted to profile seen in normal animals) ECM composition, inflammation, including cytokine, ROS and MMP levels, and endothelial function in the metabolic syndrome animals. In contrast, delivery of the biological inhibitor of miR-145 (antimiR-145) to the normal animals resulted in induction of the synthetic VSMC phenotype, which produced the ECM composition, inflammatory profile, ROS and MMP production, and endothelial dysfunction similar to that observed in JCR rats. Therefore, we hypothesize that restoration of physiological VSMC miR-145 levels in the late stage of CCG in the metabolic syndrome restores CCG by normalizing ECM composition and inflammation and restoring endothelial function.
Three specific aims will be addressed: 1) determine whether VSMC-specific miR-145 delivery normalizes ECM remodeling during CCG in the metabolic syndrome, 2) determine whether VSMC-specific miR-145 delivery and normalized ECM remodeling ameliorate excessive inflammation (inflammatory cell infiltration, cytokine, ROS and MMP production from these cells) during CCG in the metabolic syndrome, and 3) determine whether VSMC-specific miR-145 delivery and normalized ECM remodeling restore endothelial function during CCG in the metabolic syndrome. These in vivo studies will identify functional physiological responses, which account for miR-145's global effect on CCG recovery, at the cellular level.
People with metabolic syndrome are at high risk for heart attacks, in part because they fail to grow collateral vessels in response to stable angina (chest pain). We have recently used a small RNA molecule (microRNA) to successfully stimulate collateral vessel growth in a rat model of metabolic syndrome. This intervention has high potential for prevention of heart attacks in humans, but the mechanisms by which this microRNA was able to induce collateral growth must first be understood. This is the goal of this proposal.
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